Screen impeller

ABSTRACT

An impeller for installation within a pulp screening machine in which each blade of the impeller is provided with a white water dilution channel communicating with the hollow shaft for the purpose of projecting streams of white water against the inner face of the screen. These dilution channels are located in the same axial position on each set of radially opposite blades and on adjacent blades the dilution channels are offset longitudinally by one width of channel so that each longitudinal strip of the screen plate is cleaned by two dilution channels.

United States Patent Cowan [54] SCREEN IMPELLER [72] Inventor: Ben Cowan, 5460 Connaught Ave., Montreal, 29 Quebec, Canada [22] Filed: Oct. 27, 1969 211 Appl. No.: 869,642

[30] Foreign Application Priority Data Sept. 19, 1969 Canada ..62,526

[52] U.S. Cl ..209/273, 209/306 [51] Int. Cl ..B07b 1/04 [58] Field of Search ..209/273, 306, 305, 300, 250;

[56] Reierences Cited UNITED STATES PATENTS Cowan et al. ..209/273 [451 Jan. 25, 1972 Henius ..210/403 X Hornbostel ..210/403 X Primary Examiner-Tim R. Miles Assistant Examiner-William Cachlinski, Jr. Attorney-Fetherstonhaugh & Co.

57 ABSTRACT An impeller for installation within a pulp screening machine in which each blade of the impeller is provided with a white water dilution channel communicating with the hollow shaft for the purpose of projecting streams of white water against the inner face of the screen. These dilution channels are located in the same axial position on each set of radially opposite blades and on adjacent blades the dilution channels are offset longitudinally by one width of channel so that each longitudinal strip of the screen plate is cleaned by two dilution channels.

7 Claims, 6 Drawing Figures PATENTEU M825 1972 SHEEI 1 BF 5 INVEN TOR Ben COWAN PA TEN'I' A GEN TS FATENTEDJANZSHYZ 35370077 sum BM 5 INVEN TOR Ben ICOWAN PATENT AGENTS 34 1 FIG. 5

INVENTOR Ben CGWMM im z y 5 PA TENT AGENTS SCREEN IMPELLER This invention relates to an improved rotor for use in pulp screens, and particularly to means whereby dilution water is projected from the hollow rotor shaft in controlled amounts towards the inner surface of the screen throughout a substantial portion of its length.

In particular this invention is an improvement over the rotor illustrated in my Canadian Pat. No. 634,122, issued on Jan. 9, 1962, wherein dilution water was directed from the hollow shaft of the rotor through a series of radiating channels disposed midway of the length of the rotor. The flow of water along the length of the rotor blades was uncontrolled, and dilution water may not be applied to the face of the screen where it would be most effective.

To remedy this drawback in Canadian Pat. No. 634,122 it is proposed, in the present application, to provide a dilution water channel on the back of each blade of this rotor, the channels being approximately 6 inches wide and about three fourths of an inch deep. Each channel would be supplied with white water from the hollow shaft of the rotor through two apertures in the wall of the shaft. To improve the penetration of the white water through the pulp mat to the screen surface, the end of the channels may be closed off with a bar leaving only a narrow slot for the opening. By this means the velocity of the white water can be increased for more penetration through the pulp mat and a better cleaning effect on the screen plate.

Dilution channels are located in the same axial position on each set of radially opposite blades. On adjacent blades the channels are offset by one (l) width of channel, so that each longitudinal strip of screen plate is cleaned by two (2) dilution channels.

In order to control the rate of flow of white water to the system, a uniform pressure differential is required between the white water supply and the point of discharge. For this purpose a differential pressure controller will be installed between the screen feed chamber and the white water supply line, with a control valve to maintain a fixed pressure drop between the two. This will keep a uniform volume of white water flowing for dilution and cleaning.

The primary object of the invention is to provide a more uniform flow of dilution water along a substantial length of the screen.

A further object of the invention is to provide means whereby the dilution water is directed towards the inner surface of the screen in a series of longitudinal jets at opposite sides of the screen rotor.

A further object of the invention is to provide means whereby the individual jets have a controlled longitudinal orifice to provide a long narrow jet of dilution water at high velocity.

A still further object of the invention is to provide means whereby a fixed pressure drop between the screen feed chamber and the dilution water supply maintains a uniform flow of dilution water to the screen face.

These and other objects of the invention will be apparent from the following detailed specifications and the accompanying drawings in which:

FIG. 1 is a longitudinal vertical section of a pulp screen showing in full elevation an impeller according to the present invention.

FIG. 2 is a longitudinal section of the impeller shown in FIG. 1.

FIG. 3 is a transverse section of the impeller taken on the line 3-3 of FIG. 2.

FIG. 4 is a schematic expanded plan view of the rotor blades, showing the relative longitudinal location of the dilution channels.

FIG. 5 is an enlarged outer end view of one of the dilution channels.

FIG. 6 is a vertical section taken on the line 66 of FIG. 5.

Referring to the drawings, the pulp screen 5 is a typical example of such a machine and has a housing 6 having a pulp inlet 7 and a discharge 8.

An annular screen 9 is mounted within the housing 6 and is supported between an external end plate 10 and an internal end plate 111.

An impeller assembly 12 includes a shaft 13 and a series of blades 14 radiating outwards from the shaft. The shaft 13 includes a hollow portion 15 and a stub shaft 116 and is mounted for rotation, coaxially with the screen 9', in the bearings 17 and 118.

On the back of each of the rotor blades 14, that is on the side of the blade opposite from the direction of rotation, there is provided a rectangular channel 19 extending the full depth of the blade from the surface of the shaft 13 to the outer edge 20 of the blades. The interior of each of the channels 119 are in communication with the interior 211 of the hollow portion 15 of the shaft 13 by means of the apertures 22. The ends 23 of the channels adjacent the screen 9 are open to form a water discharge nozzle.

The channels 19 are disposed longitudinally of the impeller 12 in order to distribute the white water to the best advantage along the interior of the screen 9, as shown particularly in FIGS. 1 and 4. These dilution channels 19 are located in the same axial position on each set of radially opposite blades 14. On adjacent blades the channels 19 are offset longitudinally by one (1) width of channel so that each longitudinal strip of the screen plate 9 is cleaned by two (2) dilution channels 19.

In order to make the disposition and longitudinal location of the channels 119 clear, each of the blades 14 in FIG. 3 have been lettered A through I opposite their outer tips, and the blades shown schematically in FIG. 4 have been identified with the lettered blades shown in FIG. 31.

In FIGS. 5 and 6 there is shown means to improve the penetration of the white water, from the channels 119, through the pulp mat to the surface of the screen 9. The ends of the channels 19 are partially closed off by a bar 24, leaving only a longitudinally disposed narrow slot or nozzle 25. By this means the velocity of the white water can be increased for more penetration through the pulp mat and a better cleaning effect on the screen plate.

In order to control the rate of flow of white water to the system, a different pressure control is required between the white water supply through the hollow portion of the shaft 13 to the channels 19 and the discharge 8 from the machine. For this purpose a differential pressure controller will be installed between the screen feed inlet chamber 7 and the white water supply line to the hollow shaft 13, with a control valve to maintain a fixed pressure drop between the two points.

This will keep a uniform volume of white water flowing for dilution and cleaning. The differential pressure controller and the control valve are not shown as these are well known in the art.

By ensuring that a constant and controlled flow of white water is maintained along a major portion of the screen, providing maximum penetration of the white water through the pulp mat, a maximum separation of the good fibers from reject material is obtained so that, with the good fibers being carried through the screen and consequent cleaning of the screen by the multiple jets of white water, located axially along the blades the reject material, stripped of all good fiber, is readily carried away through the reject discharge opening 28.

The embodiments of the invention :in which an exclusive property or privilege is claimed are defined as follows:

1. In a pulp screen apparatus comprising a housing, a drum screen having an inlet end and a discharge end through said housing, inlet means for feeding pulp through said inlet end to the interior of said screen, means for discharging a reject fiber fraction from the interior of said drum discharge end, and means for discharging an accepts fiber fraction that passes through said screen from said housing, the improvement comprising an impeller comprising a shaft having at least a portion thereof hollow to form a white water supply duct, means for supplying white water to said duct, a series of blades mounted longitudinally on said shaft and extending substantially the length of said screen between said ends and radiating outwardly therefrom to a position adjacent the inner surface of said drum screen, a channel on one face of each of said blades, said channels communicating at their inner ends with said water supply duct and extending radially so that their outer ends are at the outer edges of said blades, said channels being separately disposed axially along the length of said shaft and being circumferentially offset relative to each other to project streams of white water radially against the inner surface of said drum screen.

2. An impeller as set forth in claim 1 in which said channels are of rectangular shape and narrow depth in a direction normal to the plane of the blades, the channel on one blade being offset axially by the width of the channel on the next adjacent blade.

3. An impeller as set forth in claim 1 in which said channels on radially opposite blades are in the same radial plane.

4. An impeller as set forth in claim 1 in which outlets of said channels are restricted to provide a narrow axially aligned nozzle.

5. An impeller as set forth in claim I in which the channels are located on the face of the blades opposite from the direction of rotation of the impeller.

6. An impeller as set forth in claim 1 in which the channels are disposed axially of the impeller from approximately onethird of the length of the impeller from the inlet end of the screen towards the discharge end of the screen.

7. An impeller as set forth in claim 1 in which said channels have a width axially of the blades of about 6 inches and a depth from the face of the blades of about three-quarters of an inch. 

1. In a pulp screen apparatus comprising a housing, a drum screen having an inlet end and a discharge end through said housing, inlet means for feeding pulp through said inlet end to the interior of said screen, means for discharging a reject fiber fraction from the interior of said drum discharge end, and means for discharging an accepts fiber fraction that passes through said screen from said housing, the improvement comprising an impeller comprising a shaft having at least a portion thereof hollow to form a white water supply duct, means for supplying white water to said duct, a series of blades mounted longitudinally on said shaft and extending substantially the length of said screen between said ends and radiating outwardly therefrom to a position adjacent the inner surface of said drum screen, a channel on one face of each of said blades, said channels communicating at their inner ends with said water supply duct and extending radially so that their outer ends are at the outer edges of said blades, said channels being separately disposed axially along the length of said shaft and being circumferentially offset relative to each other to project streams of white water radially against the inner surface of said drum screen.
 2. An impeller as set forth in claim 1 in which said channels are of rectangular shape and narrow depth in a direction normal to the plane of the blades, the channel on one blade being offset axially by the width of the channel on the next adjacent blade.
 3. An impeller as set forth in claim 1 in which said channels on radially opposite blades are in the same radial plane.
 4. An impeller as set forth in claim 1 in which outlets of said channels are restricted to provide a narrow axially aligned nozzle.
 5. An impeller as set forth in claim 1 in which the channels are located on the face of the blades opposite from the direction of rotation of the impeller.
 6. An impeller as set forth in claim 1 in which the channels are disposed axially of the impeller from approximately one-third of the length of the impeller from the inlet end of the screen towards the discharge end of the screen.
 7. An impeller as set forth in claim 1 in which said channels have a width axially of the blades of about 6 inches and a depth from the face of the blades of about three-quarters of an inch. 